The present invention is a process for the disproportionation of arylsilanes using a phenylborane as a catalyst. The process uses sodium borohydride to activate the phenylborane catalyst, thereby reducing the induction time associated with the use of the phenylborane catalyst. The present process is especially useful for the disproportionation of phenyldichlorosilane to diphenyldichlorosilane and dichlorosilane.
It is known that Friedel-Crafts type catalysts taken from the group consisting of aluminum and boron chloride can catalyze the addition of benzene to trichlorosilane. For example, Barry, U.S. Pat. No. 2,626,266, issued Jan. 20, 1953, describes a process for reacting a benzenoid hydrocarbon with trichlorosilane in the presence of a boron halide to form a benzenoid substituted chlorosilane. In addition, Barry, U.S. Pat. No. 2,626,267, issued Jan. 20, 1953, describes the use of aluminum chloride to catalyze the addition of a benzenoid hydrocarbon to trichlorosilane.
Wright, J. Organomet. Chem. 145: 307-314, 1978, suggests that phenylborane catalysts may be superior to boron halide catalysts for the addition of benzene to trichlorosilane.
Wagner, U.S. Pat. No. 2,746,981, issued May 22, 1956, teaches the preparation of diaryldichlorosilanes by heating monoaryldichlorosilanes in the presence of a Friedel-Crafts type catalyst taken from the group consisting of aluminum or boron chloride.
Japanese Patent No. 263189, Pub. 1987, teaches a process where arylboranes, for example, triphenylborane is used to catalyze the disproportionation of aryldihalosilanes under conditions of reduced pressure. Running the process at reduced pressure is reported to increase the yield of diarylhalosilane.
Generally, aluminum halides have been preferred as a catalyst for the disproportionation of arylhalosilanes. The reason for this preference is the apparent faster rate of reaction associated with aluminum halide as compared to boron halides. However, aluminum halide catalysts have disadvantages in that (1) the aluminum halide must be deactivated before products can be distilled, (2) the aluminum halide can contaminate the process with aluminum salts, and (3) the aluminum halide leaves a solid-liquid distillation residue. Since phenylborane compounds are soluble in the arylsilanes used in the disproportionation process, their use could alleviate problems described with the use of aluminum halide catalysts. However, phenylborane compounds demonstrate a latent period before the disproportionation reaction occurs, thus extending the time required for disproportionation to occur.
The inventors have found that sodium borohydride can activate phenylborane compounds, thereby reducing the latent period and making the phenylborane compounds more desirable as catalysts for the disproportionation of arylsilanes.